Specific language- impaired (SLI) children display inordinate difficulties learning language in the relative absence of behavioral, neurological, oral-motor, cognitive, or sensory deficits. One area of language acquisition that is especially problematic for these children is grammatical morphology, including auxiliary verbs, for example is and will, an inflections, for example the past tense -ed and the third person singular -s in walks. SLI children's difficulty with grammatical morphology persists even though they are reared in environments where language interactions are similar to those of normally-developing (ND) children. These children are at significant risk for communicative difficulties throughout the school years and across the life span which affect areas of life functioning associated with communication, such as academic and social development. The aim of this proposal is to obtain a better understanding of how SLI children benefit from the language in their environment. The specific questions concern whether SLI children utilize linguistic input as efficiently and to the same extent as younger ND children with similar language skills. To examine these questions, two groups of SLI and younger ND children will participate in an enrichment program in which dense concentrations of two auxiliary verb, is and will, will be presented in yes-no questions. SLI and ND control groups will not receive more frequent examples of auxiliaries. After a two-month experimental period, the children's language productions will be monitored for an additional six months to determine if broader changes in the children's grammatical systems occur. Evaluation of the effects of the enrichment program across time will provide important insights into the nature of specific language impairment and the role of input in the acquisition of grammar. The research asks: Does concentrated exposure of is and will facilitate the SLI children's acquisition of these auxiliaries? Does concentrated exposure of is and will foster SLI children's acquisition of other auxiliaries (for example, can, might, should, was, are)? Does concentrated exposure of is and will foster SLI children's acquisition of non-auxiliary grammatical form that are theoretically related to auxiliaries (for example, obligatory usage of sentence subjects, nominative case marking of subject pronouns, third person singulars)? Do the patterns of learning for the SLI children differ from those of ND children at any of the three levels?